Docosahexaenoic acid (DHA)

Docosahexaenoic acid (DHA) is an omega-3 fatty acid. It is found in cold water fatty fish, such as salmon. It is also found in fish oil supplements, along with eicosapentaenoic acid (EPA). Vegetarian sources of DHA come from seaweed.

Your body needs DHA for the proper functioning of your brain as an adult, and for the development of your nervous system and visual abilities during the first 6 months of life. In addition, omega-3 fatty acids are part of a healthy diet that helps lower risk of heart disease.

Our bodies naturally produce small amounts of DHA, but we must get the amounts we need from our diet or supplements. Most people in the Western world do not get enough omega-3 fatty acids in their diet.

Because omega-3 fatty acids are needed for children's brains to develop properly, researchers have examined whether fish oil might reduce ADHD symptoms. So far, results have been mixed. One study showed fish oil might help, but many patients dropped out of the study before it was completed.

Depression

Although some studies have shown that fish oil reduces symptoms of depression, it isn't clear whether DHA alone has the same effect. Other studies suggest it may be EPA which has the positive effect on depression.

Heart Disease

Fish oil appears to have positive effects on existing heart disease. It also may lower the risk for developing heart disease. Omega-3 fatty acids found in fish oil help lower triglycerides (fats in the blood), lower blood pressure, reduce the risk of blood clots, improve the health of arteries, and reduce the amount of arterial plaque, which narrows arteries and causes heart disease. The American Heart Association recommends eating fish, particularly fatty fish, at least two times a week. Fatty fish include salmon, herring, lake trout, sardines and albacore tuna. People with existing heart disease may need fish oil supplements in addition to adding more fish to their diet. Ask your doctor if fish oil supplements would be right for you.

Infant Development

DHA plays a crucial role in the growth and development of the central nervous system as well as visual functioning in infants.

Rheumatoid Arthritis

Several small studies indicate that fish oil may help reduce symptoms and inflammation associated with rheumatoid arthritis. However, it does not stop joint damage from getting worse.

Menstrual Pain

Fish oil appears to reduce the pain of menstrual cramps when taken on a regular basis (not just when menstruating).

Raynaud Syndrome

Several studies show that high doses (12 g) of fish oil can reduce sensitivity to cold in the fingers and toes of people with Raynaud syndrome. Doses this high should be taken only under a doctor's supervision.

Lupus

Two small studies suggested that fish oil reduced fatigue and joint pain associated with lupus.

DHA is found in cold water fatty fish, including salmon, tuna (bluefin tuna have up to five times more DHA than other types of tuna), sardines, shellfish, and herring.

Although some of these fish contain low levels of mercury, the Food and Drug Administration has found that consuming several servings of fish each week poses no risk to healthy people and conveys many health benefits.

Women who are pregnant or planning to become pregnant should avoid king mackerel, shark, swordfish, and tilefish. They should also limit consumption of white albacore tuna to under 6 oz. per week.

High-quality fish oil supplements made by manufacturers who test for mercury and other toxins do not pose the same risk of mercury contamination. Read labels carefully and check for purity, or ask your doctor to help you find the best quality DHA supplement.

For infants, breast milk from a mother who eats a healthy diet contains significant amounts of DHA. Infant formula may or may not have any DHA. Read labels carefully to find a brand that does.

Babies who are breastfed should get enough EPA if their mothers are getting enough EPA in her diet.

Adult

Most studies have used 1,000 - 2,500 mg of DHA per day.

In the diet: 2 - 3 servings of fatty fish per week, which corresponds to 1,250 mg EPA and DHA per day.

Fish oil supplements: 3,000 - 4,000 mg standardized fish oils per day. Read the label to check levels of DHA and EPA, which are not the same as mg of fish oil. People who take blood-thinning medication, such as warfarin (Coumadin) or aspirin, or people who have hemophilia should check with their doctors to determine a safe dose.

Fish oil capsules contain both DHA and EPA. Supplements containing EPA may not be recommended for infants or small children because they upset the balance between DHA and EPA during early development. Pregnant women should talk to their doctor before taking fish oil supplements.

Fish oil capsules may cause minor side effects, such as loose stools, stomach upset, and belching.

They may prolong bleeding time slightly. If you take blood-thinning medication, talk to your doctor before taking fish oil.

Blood pressure medication -- DHA may lower blood pressure, so it could make the effects of prescription blood pressure medication stronger.

Anticoagulants (blood thinners) -- EPA in fish oil supplements may increase bleeding time, so fish oil could make the effects of these drugs stronger. The same does not appear to be true of DHA alone. Blood thinners include warfarin (Coumadin) and aspirin.

Diabetes medications -- Theoretically, fish oil supplements may lower blood sugar levels and could make effects of diabetes drugs stronger. If you have diabetes, talk to your doctor before taking fish oil.

Aspirin -- Combined with aspirin, fish oil could help treat some forms of heart disease. However, this combination may also increase the risk of bleeding. Talk to your doctor to see if this combination is right for you.

Cyclosporine -- Omega-3 fatty acids may reduce some of the side effects of cyclosporine, which is often used to stop rejection in transplant recipients. Talk to your doctor before adding any new herbs or supplements to the medication you already take.